The Dose Makes A Difference

August 31, 2000

Environmental activists such as Greenpeace and Health Care Without Harm say chemicals used to soften normally-rigid PVC, or polyvinylchloride plastics, pose a threat to human health, and should be banned.

Greenpeace suggests two such chemicals, called phthalates (pronounced thall-eights), are suspect as human cancer-causing agents, could damage the liver and kidneys, might damage the development of reproductive organs, and might interfere with development by mimicking the sex hormone estrogen.

For DEHP, a plasticizer used in manufacturing medical devices, the difference between human doses and harmful animal doses are generally large:

Over a lifetime, a DEHP dose of 50 milligrams per kilogram of body weight per day can cause low level cancerous changes and liver enlargement in rats; but people at the high end of DEHP exposure (via dialysis) get a short term dose that is seven times less.

A lifetime DEHP dose of 200 milligrams per kilogram of body weight per day can cause shortened lifespans or weight loss in rats; but people exposed to DEHP via dialysis get a short term dose that is 28 times less.

A lifetime DEHP dose of 400 milligrams per kilogram of body weight per day can cause liver tumors in rats; but people exposed to DEHP via dialysis get a short term dose 56 times less.

For DINP, a plasticizer used in softened-vinyl toys for children -- but no longer used in pacifiers or chew-toys -- a lifetime dose of 88 milligrams per kilogram of body weight per day led to only a low level of observed adverse health impacts on male rats. Children using pacifiers for two years would be exposed to a dose 6,000 times less.